Apparatus for manufacturing resistors



March 22, 1966 c. l.. WELLARD APPARATUS FOR MANUFACTURING RESISTORS 2 Sheets-Sheet 1.

Filed June l, 1964 INVENTOR CHARLES L. WELLARD l ATToRNEY March 22, 1966 3,241,452

C. l... WELLARD APPARATUS FOR MANUFACTURING RESISTORS Filed June 1, 1964 2 Sheets-Sheet 2 FIG. 2

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. IMPEDANCE ad 215 To CONTROL AMPuHER-ej RESISTOR T0 BE CUT United States Patent D 3,241,452 APPARATUS FOR MANUFACTURING RESISTQRS Charles L. Weilard, Wayne, Pa., assigner to American Components, Inc., a corporation of Pennsylvania Filed June 1, 1964, Ser. No. 371,712 14 Claims. (Cl. 90-11.62)

This invention relates to apparatus for the manufacture of resistors and more particularly to apparatus for the manufacture of helically cut resistors.

Helically cu-t resistors have heretofore been manufactured by semi-automatic processes, and in general these processes have followed a routine which will be described below.

First, it should be understood, that the blank resistors, i.e. the resistors from which the helical resistors are cut, are fabricated in batches and each blank resistor in a given batch does not have the same nominal value. For instance if a batch of blank resistors is produced under conditionswhich are designed to render resistors of one thousand ohms, nominal value, the batch may actually include resistors having a spread of :30% from the nominal of one thousand ohms, with the distribution resembling a gaussian distribution in which an approximately equal number are below one thousand ohms and an equal number above one thousand ohms.

Once lsuch a batch is made, the manufacturer has to sort the resistors into tighter categories, usually on the order of :5% spread and this step entails checking the resistance value of each resistor in the batch in order to place it in its correct tighter category. Having sorted the resistors as just described, the manufacturer next operates on the resistors in one of the sorted groups. For instance assume that the manufacturer wants to produce one helically cut resistor of ten thousand ohms and the blank to be worked with is from the group which has resistors of 800 ohms :5% each. The manufacturer `would take one of the resistors Ifrom the correctly classilied eight hundred ohm resistor category and place it in a lathe type device (which operates in conjunction with a grinding wheel to provide a helical-cutting machine). r1`he length and diameter of the resistor blank and the resistance value of the end product would then be considered 4in order to determine the speed of the lead screw. The foregoing consideration is necessary because the speed at which the blank is transported past the grinding wheel determines the pitch of the helical resistor path and obviously the relationship between the value of resistance desired and the value of the resistor blank will dictate the helical pitch which should be cut. According to a preferred practice it is desirable to have the helical resistance path begin at the `lirst end terminal and finish at the second end terminal, i.e. it is not desirable to leave a relatively large area of the resistor blank in a state of being uncut. As just mentioned, in order to accomplish the preferred end product, the length and diameter of the resistor blank as well `as its uncut, or blank, value must be considered. Once these parameters are determined, the lead screw motor is set at a speed which will guide the blank resistor along a cutting path of the grinding wheel to produce a helically cut resistor of the proper value and preferred embodiment, i.e, a resistor which will begin its helical path at one terminal and end at the other.

In the semi-automatic process of the prior art, the speed of the lead screw motor is determined by `consulting graphic charts upon which the end product resistance value `is plotted as a curve between an ordinate of blank resistor values and an abscissa of lead screw speeds. The operator chooses the graphic chart of the resistance value to be produced and knowing the value of the resistor blank determines the speed at which the lead screw should operate. The graphic charts are made according to blank resistor length and diameter so that the length and diameter parameters are included in choosing the proper chart.

The operator then consults a second chart to ind the potentiometer or speed control setting of the lead screw motor and makes the proper setting to effect the proper lead screw motor speed. Thereafter the grinding wheel motor, lathe motor and lead screw motor are put into operation. An ohmmeter is set up in connection with the resistor blank so that the resistance value can be read as the helical resistor is cut. When the designated value is read on the ohmmeter, the motor drives are all switched of either manually or automatically.

While the processes for semi-automatically producing helically cut resistors may vary from the foregoing process in some steps, in general the foregoing process represents the philosophy of all these prior art processes. It is clear from the foregoing description that a prior art process is subject to human error in the areas of measuring the resistors into categ-cries, of reading the charts, and in setting motor speeds. In addition the prior art process is subject to relatively high production costs because of the initial batch sort and because of the time consumed in choosing and consulting the graphic charts, all resulting in a multiple of successive operations.

The present invention eliminates the necessity of an initial batch sort and the necessity of employing graphic charts which in turn makes it possible to produce an accurately rated resistor at a reduced production cost.

Accordingly, it is an object of the present invention t0 provide an improved mechanism for producing helically cut resistors.

It is a further object of the present invention to provide an automatic method of producing helically cut resistors.

In accordance with a feature of the present invention there is provided a first resistor bridge device wherein one leg is a settable resistance means to be set to the desired value of resistance to be produced and another leg is the blank resistor from which the helically cut resistor is formed.

In accordance with another feature of the present invention a servo system is employed, with said first resistor bridge device, to set the speed of the lead screw motor in response to an error signal developed in said first resistor Vbridge device.

In accordance with another feature of the present invention `a second resistor bridge device is employed wherein one leg is a settable resistance means to be set to the desired value of resistance to be produced and another leg is -the blank resistor as it is being cut into a helical form- In accordance with another feature `of a first embodiment of the present invention a self returning switch connects the resistor blank as a leg into said first resistor bridge device and after a short period of time automatically switches to connect the resistor blank as it is being cut into said second resistor bridge device.

In accordance with yet another feature of the present invention a control amplifier is connected to said `second resistor bridge device to energize at least one solenoid which in turn moves the resistor blank being cut out of the cutting path and simultaneously activates switches to terminate the motor drives and enable the cutting table to be returned to its home position.

In accordance with a feature of a second embodiment of the present invention a means is provided to continually monitor the resistor which is being cut and to adjust the lead screw motor speed to assure the system that the resistor is cut according to a schedule which will produce a helical cut beginning at one resistor terminal and terminating at the other resistor terminal.

In accordance with a feature of a third embodiment ofthe present invention a means is provided to readily convert said first resistor bridge into said second resistor bridge and properly transmit the respective outputs.

The foregoing and other objects and features of this invention will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is an overall schematic and block diagram of one embodiment of the present invention;

FIGURE 2 is a schematic diagram of a second embodiment of the present invention to be employed with the necessary portions of the system of FIGURE l;

FIGURE 3 is a schematic diagram of a third embodiment of the present invention to be employed with the necessary portions of the system of FIGURE 1.

Before examining in detail the mechanism of the present invention let us consider the general operation. The present invention is employed to cut a blank resistor (i.e. an element comprising a non-conducting substrate With a conductive metal lm thereon, which metal film entirely encompasses the substrate as a continuous layer of metal) into a helically cut resistor. The operation entails placing the resistor blank to be cut in a lathe-like device which will hold it and rotate it as it is cut.

In a first embodiment the chucks of the lathe-like device are electrically connected to a switch and hence the resistor blank held by the chucks is connected to the switch. The switch is connected to two resistor bridges and acts to connect the resistor blank, alternatively, as a leg in each of the two bridges.

The first of the two bridges has a decade resistor device as one leg, a standard resistor as a second leg, a variable resistor as a third leg and as was mentioned above the resistor blank, through the switch, as the fourth leg. The value of resistance to which the resistor blank should be cut is set into the first decade resistor box and the error signal produced by this first resistor bridge is transmitted to a servo system.

The servo system drives the variable resistor, until the first bridge is balanced, in response to the error signal. Simultaneously the servo system drives a potentiometer which is connected to a lead screw motor. In this way the speed of the lead screw motor is set to be commensurate with the value of the resistor to be produced and the value of the resistor blank from which said resistor is to be produced.

Now the lead screw motor is connected through a lead screw to a movable table upon which the lathe-like device is mounted. In close proximity to the lathe-like device is a continually rotating grinding wheel. As the lead screw motor rotates the table is moved, thereby transporting the rotating resistor blank into the cutting path of the grinding wheel. Hence the resistor blank becomes cut into a helically cut resistor.

As the resistor blank is being cut, its changing resistance value lis measured by a second of the two previously mentioned resistor bridges. The second of the two resistor bridges has two standard resistors as two of its legs, a second decade resistor box as the third leg and the resistor blank (through the switch) as a fourth leg. The value of the resistance to which the resistor blank is to be cut -is also set in the second decade box. As long as the resistance value of the resistor blank being cut is not equal to the value set in the decade box of the second bridge there will be an error signal produced by this second bridge. As long as there is an error signal produced by the second bridge the cutting operation cont-inues and when the second bridge becomes balanced (indicating that the resistor blank has been eut to the desired value) the cutting process is terminated. The details of how this general operation is accomplished will be described in detail hereinafter.

In a second embodiment of the invention, the resistor to be cut is xed as one leg of a first bridge, which is further made up of two standard resistors as second and third legs and a decade resistor box as a fourth leg. The error signal from this first bridge is transmitted to a high impedance device from whence it is transmitted to a second resistor bridge.

The second resistor bridge of the second embodiment is made up of a standard resistor as one leg, two variable resistors as second and third legs and the high impedance as the fourth leg.

The uncut resistor blank in the first bridge initially causes a maximum error signal to be transmitted to said second bridge. The error signal from the second bridge is transmitted to a servo system which moves one of the variable resistors to balance the bridge and simultaneously moves a speed control potentiometer to set the speed of the lead screw motor in accordance with the error signal of the first bridge.

The table which moves the resistor to be cut past the grinding wheel also moves the second variable resistor of the second resistor bridge. In this way there is a continual monitor on the resistor being cut. For example as the resistor is cut, the error signal from the first bridge diminishes and simultaneously the ratios of the voltages in the second bridge change to be commensurate with the change in error signal. If the error signal reduces in proportion to the table travel, as referenced by the second variable resistor, then the second resistor bridge remains balanced. If the error signal is not reduced in proportion to the table travel, the second bridge will be unbalanced and a signal will be sent to the servo system to relocate the first variable resistor and simultaneously increase or decrease the speed of the lead screw motor. The change in speed of the lead screw motor will move the table at a new Speed which will assure that the resistor will be cut along a path which will begin at one terminal and end at the other terminal while providing the rated ohmic value.

In a third embodiment the bridges of the first embodiment are effectively combined by simply cutting out the variable resistor arm (i.e. making the variable resistor alternatively a variable resistor and a fixed resistor), and by alternatively connecting the output of the bridge to the servo system and to the control amplifier of the cutting, locating and terminating portion of the system. The alternative uses of the bridges are effected by an automatic switching arrangement.

In the following description it should be understood that the cutting, locating and terminating portion of the system is in use with all three embodiments. In general only the bridge devices will vary with the three einbodiinents, with the exception of minor changes to accommodate the connections of the bridges to the rest of the system. The invention will be primarily discussed with respect to the first embodiment but in general the description is applicable to all of the embodiments.

Consider FIGURE l, which shows a first resistor bridge ll, made up of a xed resistor 13, a decade resistor box l5, an adjustable resistor 17 and the resistor blank 19 from which the helically cut resistor is cut. Although the resistor blank 19 is shown in the figure as partially cut, assume for the purpose of understanding the operation of the resistor bridge l1 that initially the resistor blank I9 is uncut.

The resistor bridge lll is an A.C. bridge connected through contacts 29h to an A.C. source 21. One side of the A.C. source 2l is grounded as are the appropriate ends of the resistor 17 and the resistor blank 19. While the resistor bridge 11 is shown as an A.C. bridge device, it should be understood that the bridge device can be a D.C. `bridge arrangement.

The resistor bridge 11 serves to provide an error signal which is the basis for setting the speed of the lead screw motor 51. The speed of the lead screw motor 51 is set in the following manner.

Into the decade resistor box 51 there is set the value of resistance to which resistor blank 19 is to be cut. Next, the resistor blank 19 is set in the lathe chucks 23 and 25. Although the holders 23 and 25 are referred to as chucks, it `should be understood that they can be any holding mechanisms. The resistor blank 19 is connected to the ground terminal 27 and is further connected as a leg of the bridge 11 by virtue of the self restoring switch 29, The self restoring switch 29 can be any switch, such as a thermal switch, which can -be switched to one side whereat it will hold for a predetermined time, after which time it will switch back to its normally closed side. In the preferred embodiment it is a single cam timing switch which when turned on, by depressing button 28, cam-s point 31 to make contact with point 33 and simultaneously closes contacts 29h. The timing switch points 29h can be connected to complete the circuit to the main field of motor 41 instead of connecting the A.C. source 2.1 as shown.

When switch 29 is cammed to its upper side (in FIG- URE 1) so that the points 31 and 33 are closed, the resistor blank 19 is connected as a leg in the resistor bridge 11 to produce an error lsignal across the points 35 and 37. The error signal is transmitted to the servo amplifier 39 to produce an amplified error signal which in turn is transmitted to the locating motor 41. The locating motor 41 can be any one of a number of standard motor devices either A.C. or D.C. powered, but in the preferred embodiment is an A.C. two-phase motor which has the control field and main field connected to the servo amplier. The direction of rotation and the speed are dependent on the phase difference between the main field and the control field and hence the resistor arm locating mechanism, to be described hereinafter, can be moved in either of two directions.

Mechanically connected to the locating motor 41 is a tachometer generator which serves to prevent the motor from overshooting the positioning of the driven mechanisms. Although an electrical dampening device (the tachorneter generator) is shown in the figure, it should be understood that mechanical dampeners such as drag cups and the like can also be employed.

Also mechanically connected through two gear reduction boxes 43 and 45 are respectively a movable arm 47, which shorts out a portion of resistor 17, and a speed control mechanism 49. Although two reduction gear boxes are shown in FIGURE 1, it should be understood that one gear box can be used. The gear reduction devices add to the dampening effect on the servo system to prevent the settable arms of resistor 17 and speed control 49 from overshooting their respective final stations or positions.

As long as there is an error signal from the bridge 11, i.e. as long as the ratio of resistor 13 to the resistor blank 19 is not equal to the ratio of the decade box resistor 15 to the variable resistor 17, the servo amplifier 39 will provide an error signal to drive the servo motor 41. The servo motor 41 through its mechanical linkage will move the arm 47 along the resistor 17 to effect a balance of the bridge resistors. As mentioned earlier the movable arm 47 can be moved in either direction along the resistor 17 depending upon the polarity of the error signal, i.e. depending upon whether terminal 37 is positive or negative relative to terminal 35. At this same time the variable speed control 49 has been moved to a position which will regulate the lead screw motor 51 at the proper speed at a lat-er time when lead screw motor 51 is energized.

When the bridge resistor ratios have been balanced, the error signal is zero and the servo motor 41 no longer drives the movable arrn 47 or the variable speed control 49. The variable speed control 51 is not necessarily a linear change in resistance for controlling the speed of the lead screw but with proper design of the bridge device it can be a linearly changed device. It should be clear at this point that the purpose of the bridge device 11 is to set the speed control device 49 so that the speed of the lead screw motor 51 will be in accordance with the value set in decade box 15 and in accordance with the uncut value of resistor 19.

Once the speed control device 49 has been set by the bridge device 11, the switch 29 can be connected to its other side, i.e. terminal 31 can be connected to terminal 32. The switching of the transferable point 31 can be accomplished either manually or automatically. In the preferred embodiment the switch 29 is transferred automatically. As mentioned earlier, a time delay switch can be employed which has a xed delay of 1/2 second which is sufficiently long to permit the speed control 49 to be driven to its correct setting. Thereafter the transfer point 31 is switched to its other side. As will be described in more detail, the reset button 65 of resettable switch 76 is next depressed to provide power to the motors 51 and 75, and further to enable the table 83 to follow the lead screw 52.

When the points 31 and 32 are connected, the resistor blank 19 is connected as a leg of bridge 53. At the same time, the points 29b which connect the A.C. supply to the resistor bridge 11 are opened to disconnect the power source for the error signal from bridge 11.

With the resistor 'blank 19 connected as a leg in the resistor bridge 53 and with the A.C. supply 55 connected thereto, an error signal is developed across terminals 57 and 59. The error signal is transmitted to the control amplifier 61 whereas it is amplified and transmitted as a bias to hold the thyratron 63 in a cut olf state.

As long as the thyratron 63 is biased to cut off the solenoid 64 is not energized. As will be more fully explained, as long as thyratron 63 is de-energized the resistor 19 will be able to move in a path relative to grinding wheel 77 which will affect the cutting of resistor 19. In addition with solenoid 64 de-energized, the resetting of switch 76 can be effected while when solenoid 64 becomes energized the cutting operation is terminated.

The grinding motor 71, which is continuously driven by source 73, drives grinding wheel 77 through the pulleys 79 and 81 and the belt 82. Obviously, other means for transmitting the driving power to grinding wheel 71 can be used. It should also be understood that although FIG- URE l depicts a grinding wheel 77, other means of cutting, such as ultra sonic milling or sand blasting can be used.

The lathe motor acts to rotate the blank resistor 19 to effect a helical cut. It should be noted that the ground connection 27 is shown connected to the resistor blank 19 in a commutator fashion as is the terminal 24 but other means of connections can be used.

It will be recalled that the setting of the speed control 49 for the lead screw motor 51 was described earlier. Now with the power source 67 connected to the lead screw motor 51, the motor commences to rotate at a carefully selected speed. The lead screw 52 also rotates at this carefully selected speed to move the platform 83 by virtue of the plunger of lead solenoid 84 which is normally de-energized. When the lead solenoid 84 is deenergized its movable core or plunger drops into the lead screw threads and follows the threads as the lead screw 52 turns. The lead solenoid 84 being secured to the platform 83 causes it to move. As the platform 83 moves to the right, the grinding wheel 77 cuts a helical path in the resistor blank which effectively lengthens the resistance path of the resistor blank 19 and hence increases the resistance of the resistor being made from blank 19. Although the platform is described as being moved, it could remain fixed and the grinding wheel could be the movable portion of the system.

It is the increase in resistance as the blank resistor 19 is cut which is measured by the bridge 63. The value of resistance that is desired for the resistor being cut is set in the decade resistor box 85. As the resistor 19 is cut, its resistance value considered in ratio with standard resistor 67 is measured against the ratio of the decade resistor box 85 with standard resistor 89. When these ratios are equal, there is no error signal across terminals 57 and 59 and the termination process commences.

Although the resistor bridge 53 is similar to the resistor bridge 11, there is no need to provide means for detecting two different polarity error signals since the resistor blank is normally cut in the same way.

When the bridge 53 is balanced and the error signal no longer exists, the thyratron 63 fires thus energizing solenoid 64. When solenoid 64 becomes energized its plunger 66 moves out to tilt the motor 75 and the chucks 23 and 25 away from the grinding wheel 77. The movement of the shaft 78 closes the resettable switch 76. The resettable switch 76 is a mechanical latching switch with three latching points A, B, and C and one set of interrupt points D. The B points are closed when the switch is set by the movement of shaft 78 to energize solenoid 84 and the A points are opened in response to the movement of shaft 87 to interrupt the power, from source 67, being transmitted to motors 75 and 51. Hence, motors 75 and 51 stop rotating. The energization of solenoid 84 lifts its plunger 86 out of the lead screw thread and the spring 78 returns the platform 83 to its left hand side. Resettable switch 76 which is a mechanical resettable switch employs its A set of points to open the power circuit from the bridge 53 to the resistor 19 to prevent any shocks when resistor 19 is removed. The motor 75 and chucks 25 and 23 return to their normal position by gravity or can be spring loaded.

Now with the platform returned to the left hand side and with the power cut off excepting to solenoid 64, the resist-or 19 is removed and a new resistor blank inserted in the chucks 23 and 25. If a new value of resistor is to be cut, this value is placed in the decade resistor boxes and 85. Thereafter the switch button 28 is depressed causing the single cam switch 29 to operate, closing points 31 and 33 which in turn cause the bridge 11 to be active to reset the speed control 49. After the speed control 49 has been reset, the reset button 65 of resettable switch 76 is depressed to provide the power to motors 75 and 51 and to de-energize solenoid 84 which drops its plunger into the lead screw threads.

In addition the button 65, throught interrupt points D of switch 76, momentarily disconnects the anode of thyratron 63 to terminate its conduction. When button 65 is released the circuit to the anode of thyratron 63 is again connected but the bias provided by control amplifier 61 in response to the breaking of switch 76 points A and the subsequent substitution of a new resistor blank, keep the thyratron 63 biased to a cut o status.

When switch 29 closes points 31 and 32 and the power is supplied to motors 75 and 51, the cutting operation is ready to begin anew. Since the time to set speed control 49 is so fast (1/2 second) there is virtually no delay before the reset button 65 can be depressed. As was just mentioned when the reset switch 75 is reset, the motors 75 and 51 commence `operating and the bridge 53 commences producing an error signal which holds solenoid 64 in a de-energized state. With solenoid 64 de-energized, the chucks 23 and 25 move the resistor blank 19 into the path of grinding wheel 77 to be cut and the process repeats itself.

It should be noted that resistor blanks could be cut in opposite directions every other time by detecting different polarities in the error signals of bridge 53 and by providing means to transmit a phase identified signal to motor 51.

In FIGURE 2 there is shown a second embodiment of the present invention. Bridge 253 is the equivalent of bridge 53 (FIGURE 1) which provides an error signal to the control amplifier, such as control amplier 61 of FIG- URE 1. When there is no error signal, i.e, when resistor 211 is cut to produce the ohmic value set in decade box 213, the bias to the control amplifier on lines 215 will be non existent and in a manner similar to that described with FIGURE 1, the cutting process will be terminated.

The embodiment of FIGURE 2 provides a continuous monitor of the resistor being cut. The monitoring operation insures that the speed of the lead screw motor is commensurate with the value of the resistor to be cut and with the physical characteristics of the resistor blank (for instance the resistivity of the metal film on the substrate may vary).

When resistor 211 is blank, or uncut, and it is placed in bridge 253, there results a maximum error signal across points 217 and 219. The foregoing assumes that the desired value of the resistor is placed in the decade box 213.

The maximum error signal is transmitted to the high impedance device 221. The high impedance device 221 may be a differential amplifier, or a cathode follower or other similar high impedance devices, coupled to a resistor which will be equal to the value of resistor 223 when the adjustable arm has been moved the distance of the table travel. Preferably, the high impedance lshould isolate the bridge 225 from the bridge 253, so that the former does not load the latter.

The maximum error signal is transmitted from the high impedance device 221 to the bridge 225 as a signal on one leg thereof. The presence of the maximum error signal across terminals 227 and 229 will produce a maximum second error signal across terminals 231 and 233. The maximum error signal at terminals 231 and 233 will be transmitted to the servo system to adjust the variable resistor 235 and to simultaneously adjust a speed control device, such as speed control potentiometer 49 of FIG- URE 1. By adjusting the variable resistor 235 the bridge 225 will become balanced to halt the second error signal and simultaneously the speed of the lead screw motor will be determined by the adjustment of the speed control dev1ce.

Now assume that through a cutting mechanism similar to that shown in FIGURE l, the resistor 211 is subjected to being cut. As the helical pattern is cut on resistor 211 the error signal across the terminals 217 and 219 is reduced. The reduced error signal when transmitted to bridge 225 would tend to unbalance this bridge and at this point the role of the variable resistor 223 becomes significant. As the resistor 211 is being cut, the table holding the cutting mechanism moves and in turn moves the movable arm 224 of resist-or 223. This action increases the ratio between the voltage drop across resistor 237 and the drop across resistor 223 to match the increased ratio of the voltage drop across resistor 235 and the error signal.

However, the resistor 223 plays an even more signicant role. The resistor 223 is so formed that its linear characteristic matches the travel of the table. For example if resistor 211 is cut to its midway point but its resistance value is not one half of the value in the decade box then the error signal from bridge 253 will be greater than it should be. Meantime the movable arm 224 will be moved to the midway point of resistor 223 and will provide a voltage drop thereacross to compensate for an error signal from bridge 253 which would be produced if resistor 211 had a value of one half that value in decade box 213. Since resistor 211 in our last hypothetical situation does not have a value equal to one half the value in decade box 213 the bridge 225 will not be balanced and an error signal will be sent to servo amplifier 39 (FIGURE 1). In response to the error signal to servo amplier 39 (FIGURE 1) the speed of the lead screw motor will be adjusted and variable resistor 235 will be adjusted to again balance the bridge 225. It should be understood the system doesnt wait until the midway point to monitor the resistor being cut but continually monitors it and continually adjusts the speed of the lead screw motor to make certain that the resistor will be cut completely from one terminal to the other while producing the rated value resistor. In this way resistors can be produced having tolerances of =O.1%.

In FIGURE 3 there is shown an arrangement to combine the two bridges of FIGURE l into a single device. The decade resistor box 311, the fixed resistor 313 and the resistor' to be cut 315 are common to both bridges. The variable resistor 317 can be converted into a fixed resistor by opening the shorting lead 319, through points 321.

When the lead screw motor speed is to be set (as described with FIGURE l) the single cam switch 323 is turned on. At this time the variable resistor 317, through closed points 321, acts to balance the bridge. The error signal in this first phase of the operation is transmitted from terminals 325 and 327, through closed points 329 with 330 and 331 with 332 to the servo amplifier 39 as shown. The operation of the servo amplifier and servo system to adjust the lead screw motor and balance the bridge is the same as described with FIGURE 1.

When the single cam switch 323 rotates to close points 330 with 333 and 332 with 335, the points 321, 329 and 331 will be open. At this time the variable resistor 317 becomes a fixed resistor and the bridge is unbalanced. The error signal is transmitted to control amplifier 61 to effect the cutting of resistor 315 to its proper value. When resistor 315 is cut to its proper value the cutting operation is terminated and the mechanism reset as described with FIGURE 1.

While the foregoing description sets forth a principle of the invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A resistor manufacturing device comprising: a resistor blank to be cut to a predetermined value of resistance; cutting means to cut said resistor blank, said cutting means including variable speed control means; first and second error signal generating networks; switching means connected to said resistor blank and alternatively connectable to said first and second error signal generating networks; said first error signal generating network including a movable means to be positioned to reduce an error signal produced by said first error signal generating network to zero when said resistor blank is connected thereto through said switching means; positioning means connected to receive an error signal from said first error signal generating network and connected to physically position said movable means of said first error signal generating network to effect a zero error signal and simultaneously to position said variable speed control means of said cutting means in accordance with the error signal produced by said first error signal generating network; said second error signal generating network producing an error signal when said switching means connects said resistor blank thereto until the resistor blank is cut to said predetermined value of resistance; circuitry means connecting said second error signal generating network to said cutting means to drive the same for as long as there is an error signal from said second error signal generating network and in accordance with said variable speed control means.

2. A resistor manufacturing device according to claim 1 wherein said cutting means includes a lathe device to hold said resistor blank; a movable table means upon which said lathe device is mounted; and a cutting device disposed in close proximity to said lathe device so that as said movable table means moves said lathe device past said cutting device a resistor blank held by the former will be helically cut.

3. A resistor manufacturing device according to claim 2 where said movable table means includes a solenoid with a movable core secured thereto and a lead screw assembly, the movable core of said solenoid being in an engaging and disengaging relationship with said lead screw assembly.

4. A resistor manufacturing device according to claim 3 wherein said variable speed control means is connected to said lead screw assembly to effect a speed control thereof.

5. A resistor manufacturing device according to claim 1 wherein said first and second error generating networks are resistor bridge networks, each. of which has one resistor leg that can be set to a resistance value equal to said predetermined value of resistance to which said resistor blank is to be cut.

6. A resistor manufacturing device according to claim 1 wherein said switching means is a time controlled switching means which is transferred to one side for a predetermined time and automatically returned to a second side after the elapse of said predetermined time.

7. A resistor manufacturing device according to claim 1 wherein said positioning means includes a servo system.

3. A resistor manufacturing device according to claim 1 wherein said circuitry means includes a switching element held inoperative by said error signal of said second error signal generating network and further includes a solenoid switch arrangement connected to be activated by said switching element when said last mentioned error signal ceases.

9. A resistor manufacturing device comprising: means to hold a resistor blank, said resistor blank to be cut to a predetermined Value of resistance; cutting means t0 cut said resistor blank, said cutting means disposed in close proximity to said means to hold; transport means coupled to said means to hold and including controllable speed means to control the speed at which said transport means moves said means to hold past said cutting means; first and second error signal generating means; switching means connected to said means to hold and alternatively to said first and second error signal generating means to connect said resistor blank into either said first error signal generating means or into said second error signal generating means; a servo system connected to said first error signal generating means and to said controllable speed means to set said controllable speed means at a particular setting in response.` to the uncut value of resistance of said resistor blank when said switching means connects said resistor blank to said first error signal generating means; circuitry means connecting said second error signal generating means to said transport means and to said means to hold to effect the termination of the cutting of said resistor blank in response to the cessation of an error from said second error signal generating means when said switching means has connected sai-d resistor blank to said second error signal generating means.

10. A resistor manufacturing device comprising: rst and second error signal generating means each includ ing an associated settable means in which the value of the resistor to be cut can be set; switching means to connect a resistor blank to be cut to a predetermined value, alternatively into said first and second error signal generating means; cutting means to cut said resistor blank including control means to regulate the pattern to which said resistor blank is cut; servo system means connecting said rst error signal generating means to said control means to set control means in accordance with the value of the resistance to which said resistor blank is to be cut; circuitry means connecting said second error signal generating means to said cutting means to cause said cutting means to cut said resistor blank in accordance with the value set in said associated settable means of said second error signal generating means.

11. A resistor manufacturing device comprising: error signal generating means capable of generating first and second error signals; means to hold a resistor blank to be cut to a predetermined value, said last mentioned means connected as part of said error signal generating means; settable means connected as part of said error signal generating means in which said predetermined value can be stored; cutting means to cut said resistor blank including control means to regulate the pattern to which said resistor blank should be cut; first circuitry means connecting said rst error signal to said control means to set said control means in accordance with said predetermined value and the uncut value of said resistor blank; and second circuitry means connecting said second error signal to` said cutting means to cause said cutting means to cut said resistor blank until said resistor blank has a resistance value equal to said predetermined value.

12. A resistor manufacturing device according to claim 1l wherein said error signal generating means further includes a means to monitor said resistor blank as it is being cut and to adjust said control means to assure that a correct pattern will be cut.

13. A resistor manufacturing device according to claim 11 wherein there is included a switching means which switches said first and second error signals respectively to said first and second circuitry means.

14. A resistor manufacturing device comprising: a first resistor bridge including a settable resistor leg and including as a second leg a resistor blank to be cut to a predetermined value, said predetermined value being stored in said settable resistor leg; a high impedance means; a second resistor bridge including said high impedance means as one leg, a fixed resistor as a second leg and first and second adjustable resistors respectively as third and four legs; said first resistor bridge producing a first error signal as long as the resistor blank being cut does not equal said predetermined value stored in said settable means; first circuitry means connecting said first error signal to said high impedance means; cutting means to cut said resistor blank including control means to regulate the pattern to which said resistor blank should be cut; second circuitry means connecting said first error signal to said cutting means to cause said resistor blank to be cut until its value equals said predetermined value; said second resistor bridge producing a second error signal as long as said first and second adjustable resistors are not adjusted to balance said bridge; said first adjustable resistor connected to said cutting means to be adjusted as said resistor blank is cut thereby monitoring said resistor blank as it is cut to assure that its value at instant of time is commensurate with the length of the path cut on said resistor blank; said second adjustable resistor connected to said control means to be adjusted in accordance with the proper speed of said cutting means; third circuitry means connecting said second error signal to said control means to adjust said control means in accordance with the signal from said high impedance and the monitoring signal across said first adjustable resistor.

References Cited by the Examiner UNITED STATES PATENTS 3,105,288 10/1963 Johnson et al. 90-ll.62

WILLIAM W. DYER, IR., Primary Examiner. 

1. A VARIABLE RESISTOR COMPRISING: A HOUSING; A BASE OF NONCONDUCTIVE MATERIAL SUPPORTED BY THE HOUSING; A RESISTIVE PATH AND A CONDUCTIVE PATH SUPPORTED BY THE BASE; A LEADSCREW ROTATABLY MOUNTED IN THE HOUSING AND EQUIPPED WITH A SCREWTHREAD; A BRIDGING CONTACT ELECTRICALLY CONNECTING THE RESISTIVE PATH TO THE CONDUCTIVE PATH; AND CONTACT DRIVING MEANS FOR CAUSING THE CONTACT TO MOVE ALONG THE RESISTIVE PATH COMPRISING: A CONTACT SUPPORTING MEMBER ROTATABLY MOUNTED IN THE HOUSING AND PROVIDED WITH TEETH AND WITH A TOOTHLESS SECTION ON ITS PERIPHERY, A U-SHAPED SLOT PROVIDED IN ONE SIDE OF THE TOOTHLESS SECTION, THE LEGS OF THE SLOT BEING WIDER THAN THE BASE OF THE SLOT, SAID TEETH BEING ARRANGED TO ENGAGE THE SCREWTHREAD ON THE LEADSCREW SO THAT ROTATION OF THE LEADSCREW WILL ROTATE THE CONTACT SUPPORTING MEMBER; RESILIENT MEANS DISPOSED IN SAID U-SHAPED SLOT OF THE TOOTHLESS SECTION, SAID RESILSIENT MEANS COMPRISING A USHAPED SPRING HAVING TWO LEGS AND A BIGHT SECTION WITH THE LEGS EXTENDING OUTWARDLY FROM THE MEMBER AND IN POSITION TO ENGAGE THE THREAD ON THE LEADSCREW AS THE MEMBER IS ROTATED; STOP MEANS ARRANGED TO LIMIT THE ROTATION OF THE MEMBER IN EITHER DIRECTION WHEN ONE OF THE LEGS OF THE U-SHAPED SPRING ENGAGES THE THREAD OF THE LEADSCREW; AND THE PORTION INTERMEDIATE THE LEGS OF THE U-SHAPED SLOT FORMING A STOP MEMBER FOR LIMITING FLEXURE OF THE LEGS OF THE SPRING TOWARD EACH OTHER FROM THE UNFLEXED POSITION. 